Optics letters最新文献

This Letter describes a method for synthesizing arbitrary biaxial metamaterials based on an interleaved metallic patch-rod structure. By tailoring the patch lengths and rod spacing, the effective permittivity tensor (ε_x, ε_y, ε_z) can be independently engineered while maintaining μ≈1. The suggested structure exhibits nearly dispersionless, low-loss electromagnetic behavior by operating in the deeply subwavelength regime. The homogenization model is validated through full-wave simulations that show excellent agreement between the synthesized and equivalent bulk media. Although our approach has been demonstrated in the microwave region, it is scalable to terahertz and optical frequencies and hence represents a general framework for designing anisotropic media with a customizable biaxial response.

Hydrogen sensing is crucial for safely utilizing hydrogen gas (H₂). The soft substrate can effectively accommodate the expansion stress of palladium (Pd) film during hydrogenation, thereby transforming the gas-matter reaction into a light-matter interaction. This mechanism significantly enhances the optical response of H₂ absorption of the Pd film while enabling direct visualization of this process. Here, we introduce a hydrogen-tunable Fabry-Pérot (FP) resonator (HTFPR) comprising a PMMA/Pd bilayer on a soft spacer and a Pd mirror. The absorption/desorption of H₂ on the resonator exhibits repeatable and tunable modulation of FP resonance based on the surface wrinkling of the Pd film, leading to color variation. By optimizing the structural parameters, the resonator achieves an extremely high reflectance variation of approximately 43% with a response time of about 5 s in 4% H₂ mixed with air, which can be applied in visual hydrogen sensing. Furthermore, the resonator demonstrates great repeatability and selectivity towards H₂. These results indicate that the tunable Fabry-Pérot resonator is suitable for practical hydrogen detection.

We propose an Au-free Ti/Al/TiN Ohmic contact on an n-type Al_0.57Ga_0.43N epitaxial layer and utilize it in deep-ultraviolet light-emitting diodes with improved efficiency. The surface morphology, chemical stoichiometry, and electrical performance of the proposed contact are thoroughly investigated and compared with those of conventional Ti/Al/Ni/Au electrodes. The Ti/Al/TiN stack exhibits a specific contact resistivity of 3.41 × 10^-4 Ω·cm² at optimized annealing conditions, which is 26.5% lower than that of the conventional Ti/Al/Ni/Au stack (4.64 × 10^-4 Ω·cm²). A smoother surface morphology and the absence of phase separation are identified in the proposed Ti/Al/TiN design, attributed to the low diffusivity of TiN into other metal alloys and its strong thermal stability as a binary compound.

White organic light-emitting diodes (WOLEDs) employing ultrathin emitting layers (UEMLs) have received more attention due to their simple properties. However, UEMLs-based WOLEDs still suffer from severe efficiency roll-off and poor operational lifetime. Herein, we propose an innovative interlayer strategy to construct high-performance WOLEDs comprising blue fluorescent and orange phosphorescent UEMLs. Utilizing what we believe to be a novel TADF-based co-host interlayer, the resulting device achieves extremely low-efficiency roll-off of only 1.7% and a superior T₅₀ operational lifetime of 3319.2 h at 1000 cd/m², among the best values reported so far for hybrid WOLEDs. It also shows excellently stable spectra and a maximum power efficiency of 54.7 lm/W. The high performance should be attributed to more balanced carrier transport as well as efficient Förster energy transfer. We believe our findings present a new strategy to develop high-performance UEMLs-based WOLEDs.

Thin-film lithium niobate (TFLN) has emerged as a compelling platform for photonic integrated circuits. However, the realization of electrically pumped on-chip laser sources remains a critical challenge. In this work, we demonstrate heterogeneously integrated single-mode III-V-on-TFLN lasers employing a narrowband Bragg grating in combination with a Sagnac loop reflector (SLR) to provide wavelength-selective optical feedback. Through precise tailoring of the distributed Bragg reflector (DBR) grating period, controlled lasing wavelength selection in the C-band is achieved. The fabricated devices deliver on-chip output power ~1.15 mW and maintain single-mode emission from near threshold to rollover current, with a side-mode suppression ration exceeding 35 dB in the optimum operation point. These results establish the feasibility of electrically pumped laser sources on the TFLN platform and provide a scalable pathway toward fully integrated TFLN-based transmitters and reconfigurable photonic systems.

Compact visible-band microscopy benefits from co-planar metalenses that integrate multiple numerical apertures on a single platform. Here, we demonstrate a silicon-rich nitride (SRN) metalens array operating at 660 nm, uniting NA = 0.54/0.92/0.97 within one chip. Device-level characterization confirms tight focal confinement and high focusing efficiency, arising from our tailored PECVD SRN that provides a high, tunable refractive index with low absorption. Fluorescence imaging of AF647-tagged endothelial monolayers verifies functional readiness, and the wafer-scalable process supports compact, high-NA modules for integrated bio-imaging systems.

We report a noncollinear (NCL), high-power, synchronously pumped femtosecond optical parametric oscillator (OPO) based on type I (o → e + e) phase-matching (PM) inside the yz optical plane of BiB₃O₆ (BiBO) crystal. By the application of NCL PM geometry for the parametric interaction, two important goals have been achieved: 1) simplifying the wavelength tuning by transferring the full tunability (620-1030 nm for signal and 1030-3050 nm for idler) from two optical planes (xz and yz) of the biaxial BiBO crystal in the collinear PM geometry, to only one optical plane of yz, and 2) considerable shortening of the produced signal pulses (down to 33 fs at 670 nm) across the tuning range.

Tunable manipulation of focused vector vortex beams (FVVBs) in the terahertz (THz) regime is highly desirable for advanced applications in imaging, sensing, and communications, yet conventional methods often suffer from limited reconfigurability and integration capacity. In this work, we propose a dynamic metasurface platform enabling in-plane scanning of FVVBs through moiré phase engineering in two cascaded, rotatable all-silicon metasurfaces. Each layer is meticulously designed with decomposed phase profiles, combining spiral, gradient, and lens phases, to independently manipulate orthogonal circular polarization (CP) channels. By mechanically rotating the metasurfaces, we numerically demonstrate continuous lateral displacement of the focused vector beam within the focal plane, with negligible variation in focal length and robust performance under inter-layer separation changes. Furthermore, simultaneous rotation of both layers allows arbitrary positioning of the focal spot and tailored polarization symmetry. This strategy offers a versatile and compact solution for dynamic wavefront control, paving the way for adaptive THz systems with high integration capabilities.

We report a rubidium optical clock based on a new architecture in which a fiber laser is stabilized to the two-photon 5S_1/2(F=1)→5D_5/2(F^'=1) transition of ⁸⁷Rb, a choice that reduces the external field sensitivity relative to commonly used transitions. Long-term frequency fluctuation is minimized by equilibrating the helium concentration in the vapor cell, thereby suppressing collisional shifts from helium permeation. The error signal is generated through third-harmonic demodulation for the suppression of the residual amplitude modulation. With these measures, the system reaches a fractional frequency instability of 3.5×10^-13 at 1 s and 6.6×10^-15 at 10,000 s. Its long-term stability matches that of a VCH-1008 passive hydrogen maser over the same averaging time, demonstrating the potential of this compact rubidium optical clock for precision timekeeping and navigation.

Directly modulated lasers (DMLs) are extensively employed for short-reach photonic interconnection systems, but the interplay between their chirp and chromatic dispersion (CD) of standard single mode fiber (SSMF) leads to signal distortion, frequency-selective power fading, and reduced effective bandwidth. Thus, it is vital to characterize the chirp dynamic of DML. Here, we experimentally demonstrate a time-lens-based method to discriminably characterize chirp coefficients of a DML, including the adiabatic chirp coefficient κ and the linewidth enhancement factor α. Moreover, the time-lens-based setup has the dynamic observation capability of DML chirp dynamics in relation to both power and time. Experimental validation indicates that a measurement range of up to 19.9 for parameter α and 51 GHz/mW for parameter κ can be achieved, when the DML driven by a 1.33 GHz electrical signals has variable optical powers from 1.2 mW to 3.6 mW.